AQUATIC WORMS 73 



The worm now rests contentedly, hiding in the muscles so as to 

 prevent injuring its host. For it is of the greatest importance 

 to the worm that its host should live to maturity. The alder- 

 fly larva, when the time comes, changes into the mature insect. 

 It so happens that many of the mature alderflies fall a prey to 

 a black beetle known as Pterocheilus niger, and this is seem- 

 ingly what the worm expected, for the unfortunate beetle 

 must necessarily subsequently play its part in the life history 

 of this lowly worm. No sooner has the alderfly been de- 

 molished by its captor, the beetle, than the latter suffers the 

 penalty. The young Gordius now attacks its fresh host, eating 

 both organs and the fat body. Again the worm's future is far 

 fr*om a security, for the beetle must fall into the water or else 

 the worms will be unable to make their escape. It so happens 

 that some of the beetles meet with this accident. Then the 

 worms bore their way through the body of their host and 

 escape into the water, where they mature. 



Bristle-worms are members of the Polychaeta, and are often 

 found in the aquarium ; Ophryotrocha is an example. Several 

 of the Aeolosoma representatives of the Oligochaeta are usually 

 common in streams, and are most lovely creatures when ex- 

 amined under the microscope. Their body is transparent, and 

 contains beautifully coloured gold, orange, brown and green 

 globules, the colour depending on the species. 



Large numbers of worms belonging to the Naidomorpha are 

 frequently met with in the aquarium. Nais is found amongst 

 the roots of aquatic weeds ; its body is adorned with several 

 groups of bristles. It is of peculiar interest because of the 

 manner in which it buds. The bud is produced between two 

 segments of its body. This bud gradually grows to form a 

 worm, while the head and tail portion of the parent, thus 

 divided, forms a new tail anteriorly, and a fresh head pos- 

 teriorly. Further buds are produced until a long chain of 

 worms is in existence. The humour of the situation lies in 

 the fact that the head of the parent is responsible for the 

 food of the entire family, until they disperse. Dero, another 

 worm similar in appearance to Nais, has ciliated projections at 

 the posterior end of its body. 



Tubifex rivulorum is a common inhabitant of most of our 

 rivers and ponds ; it is a little red worm, and loves to burrow 

 in the mud. It does so in such a manner as to allow the tail 

 part of its body to project. Subsequently, constantly waving 

 to and fro, a continual change of water is produced. For the 

 worm breathes by obtaining air from the water and returning 

 to it the waste gases it no longer requires. 



